A 25-kg mass is suspended 4 meters above the ground. Find its potential energy. Show your work, and use the rules of significant figures when giving your answer

Potential energy due to gravitation = mass x gravity x height
= 25 x 9.8 x 4
= 980 Joules
Since the height is given to just 1 significant figure, the result should be given to 1 significant figure also.
Answer = 1000 Joules.

Instantaneous Energy Electric Field = ue(t)= ε₀(E₀*sin(kx-wt))²/2

Instantaneous Energy Magnetic Field = ub(t)= B₀(E₀*sin(kx-wt))²/2μ₀

Average Energy Density  of electric field of the wave = E₀² ε₀/4

Average Energy Density  of Magnetic field of the wave <ub>= B₀²/4μ₀

The Poynting Vector = S = ε₀*c*E₀²/2x

Explanation:  The relationship between μ₀ and ε₀ is

                                                  μ₀= 1/ε₀c²

To Poynting flux definition is provided in the image.

Average Density of the whole wave could then be found by:

                                         

                                         <u> =(E₀² ε₀/4)+ (B₀²/4μ₀)

To get to a better answer you can subsitute the relationship between μ₀ and ε₀

Remember: c = the speed of light in vacuum = 3.0 * 10⁸ m/s